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    • 专利摘要:
    The present application provides an ultra-fast EHz modulation pulse scanning laser device and a distributed optical fiber detection system, wherein by etching a plurality of phase shift gratings having different center window wavelengths on the doped optical fibers, whose interval between two adjacent center window wavelengths are preset to a fixed value, when the pump light emitted by the pump laser source enters the doped optical fiber via coupling by the multiplexer to wavelength division, using the phase shift grating etched on the doped optical fiber, a multi-wavelength narrow linewidth single-mode laser light occurs, of which the wavelength interval is preset at a fixed value; then the above light can be modulated ultra-fast by time domain control method based on electro-optical modulator (EOM), to obtain internal frequency conversion pulsed light which is continuously composed by a plurality of pulsed lights with linearly increasing frequencies, thereby forming an ultra-fast EHz demodulation. As a result, the coherence length of the laser light emitted by the laser device can be extended without changing the frequency of the laser light, thereby solving the problem of the existing distributed optical fiber detection system, namely mutual restriction. between important cues such as high spatial resolution, long distance and high frequency band. Figure for the abstract: Fig 3
    公开号:FR3098659A1
    申请号:FR1909123
    申请日:2019-08-09
    公开日:2021-01-15
    发明作者:Ying SHANG；Chen Wang；Chang Wang；Jiasheng NI；Wenan ZHAO；Chang Li；Bing CAO；Sheng Huang；Yingying Wang；Yanbin Wu
    申请人:Laser Inst Of Shandong Academy Of Science；Laser Institute of Shandong Academy of Science；
    IPC主号:
    专利说明:

    [0001] The present application relates to the field of distributed fiber optic detection technology, in particular an ultra-fast EHz (exahertz) modulation pulse scanning laser device and a distributed fiber optic detection system.
    [0002] Technical background
    [0003] Since the distributed optical fiber sensing technology can continuously detect and measure the physical parameters distributed along the length of the optical fiber, and integrate the sensing and transmission functions, it can be used to continuously measure the state information for multidimensional spatial and temporal distribution of environmental parameters distributed along the length of an optical fiber, and for further transmitting the distributed measurement information to the data processing center in real time without loss. In addition, the detection system based on distributed optical fiber detection technology has the advantages such as simple structure, convenient operation, low signal acquisition cost in a unit length and high price-performance ratio, so this technology is widely used in many important civilian and military fields such as perimeter security, pipeline leak detection, seismic wave detection and hydroponic detection.
    [0004] Distributed fiber optic sensing technology includes two technologies: Optical Time Domain Reflectometry (OTDR) and Optical Frequency Domain Reflectometry (OFDR). Compared to OTDR, OFDR has significant advantages in terms of the ultra-high spatial resolution index, in which the spatial resolution depends on the linear scan range of the laser source in the OFDR system, plus the scan range wide, the higher the spatial resolution, and ultra-high spatial resolution can be obtained when the linear scanning range of the source is wide. However, the detection distance of OFDR is limited by the optical frequency sweep time of the laser source, i.e. the longer the optical frequency sweep time, the longer the detection distance. In addition, the longer the optical frequency sweep time of the laser source, the lower the corresponding frequency, which leads to a limitation of the upper limit of the frequency of the signal to be detected.
    [0005] Therefore, as a key component of the distributed fiber optic sensing system, a problem to be solved by those skilled in the art is to improve the laser device, so as to lengthen the measurement distance of the OFDR while maintaining high spatial resolution.
    [0006] Description of the invention
    [0007] The present application provides an ultra-fast EHz modulation pulse scanning laser device and a distributed fiber optic detection system, in order to solve the problem of the existing distributed fiber optic detection system, i.e. the mutual restriction between the indices important such as high spatial resolution, long distance and high frequency band.
    [0008] According to a first aspect of the examples of the present application, it provides an ultra-fast EHz modulation pulse scanning laser device, which comprises a pump laser source, a first wavelength division multiplexer, a network of cascaded phase shift optical fiber, a second wavelength division multiplexer, a plurality of electro-optical modulators and a controller connected to the plurality of electro-optical modulators, wherein:
    [0009] the output of the pump laser source is connected to the first end of the first wavelength division multiplexer;
    [0010] the cascade phase shift optical fiber grating consists of a plurality of phase shift gratings having different center window wavelengths etched on the doped optical fibers, the interval between two adjacent center window wavelengths of which is predefined to a fixed value, and the cascade phase shift optical fiber network is connected to the second end of the first wavelength division multiplexer;
    [0011] the third end of the first wavelength division multiplexer is connected to one end of the second wavelength division multiplexer;
    [0012] the laser light emitted by each output channel corresponding to each wavelength of the second wavelength division multiplexer is transmitted respectively to one of the electro-optical modulators;
    [0013] the controller is configured to trigger by order one of the electro-optical modulators according to the predefined time interval for a predefined duration.
    [0014] Optionally, the laser device further comprises an isolator, in which:
    [0015] one end of the isolator is connected to the third end of the first wavelength division multiplexer and the other end is connected to one end of the second wavelength division multiplexer.
    [0016] Optionally, the laser device further comprises a signal amplifier, in which:
    [0017] one end of the signal amplifier is connected to the third end of the first wavelength division multiplexer and the other end is connected to one end of the second wavelength division multiplexer.
    [0018] Optionally, the cascaded phase-shifting optical fiber network consists of N doped optical sub-fibers in parallel, with N≥2, in which:
    [0019] said doped optical fiber of the cascaded phase shift optical fiber subarray is etched with a plurality of phase shift gratings having different center window wavelengths, the interval between two adjacent center window wavelengths of which is preset to first fixed value;
    [0020] the first predefined fixed value is N times the output wavelength interval of the cascaded phase shift optical fiber network.
    [0021] Optionally, the pump laser source comprises a first pump laser sub-source and a second pump laser sub-source, and the first wavelength division multiplexer comprises a first wavelength division sub-multiplexer and a second wavelength division sub-multiplexer, wherein;
    [0022] the output of the first pump laser subsource is connected to the first end of the first wavelength division submultiplexer, and the output of the second pump laser subsource is connected to the first end of the second wavelength division sub-multiplexer;
    [0023] said cascade phase-shifting optical fiber network is respectively connected to the second end of the first wavelength division sub-multiplexer and to the second end of the second wavelength division sub-multiplexer;
    [0024] the third end of the first or second wavelength division sub-multiplexer is connected to one end of the second wavelength division multiplexer.
    [0025] Optionally, the gap between two adjacent central window wavelengths is equal to or greater than 0.2 nm.
    [0026] According to a second aspect of the examples of the present application, it provides a distributed fiber optic detection system comprising an ultra-fast EHz modulation pulse scanning laser device according to the first aspect of the examples of the present application.
    [0027] Optionally, the system further comprises a circulator, a detection optical fiber, a coupler, a first interference arm, a second interference arm, a rotating Faraday mirror and a phase demodulator, in which:
    [0028] the output of the ultra-fast EHz modulation pulse scanning laser device is connected to the first end of the circulator, the second end of the circulator is connected to the sensing optical fibers, and the third end of the circulator is connected to the first end of the coupler;
    [0029] the second end of the coupler is connected to one end of the first interference arm and the second interference arm, respectively, and the other end of the first interference arm and the second interference arm is connected to the rotating Faraday mirror, respectively , the length of the first interference arm of which is not equal to that of the second interference arm;
    [0030] the phase demodulator is connected to the third end of the coupler to demodulate a phase loading caused by a disturbing signal in the detection optical fiber.
    [0031] According to the above examples, the present application provides an ultra-fast EHz modulation pulse scanning laser device and a distributed optical fiber detection system, which is characterized in that: a phase shift optical fiber network in cascade is formed by etching a plurality of phase shift gratings having different center window wavelengths onto the doped optical fibers, when the pump light emitted from the pump laser source enters the cascade phase shift optical fiber grating via coupling by the wavelength division multiplexer, multi-wavelength laser light is produced, the wavelength interval of which is preset to a fixed value; then the above multi-wavelength laser light can be ultra-fast modulated by a time domain control method based on an electro-optical modulator, to obtain an internal frequency conversion pulsed light which is continuously composed by a plurality of the linearly increasing frequency pulse lights, thereby improving the linear frequency scanning range of the laser source in the distributed optical fiber detection system and effectively ensuring the spatial resolution of the system. In addition, the coherence length of the laser light emitted from the laser device can be extended based on the narrow linewidth characteristic of the laser light emitted from the above cascade phase shift grating and ultra-fast modulation. of the electro-optical modulator, without changing the frequency of the laser light. Accordingly, the EHz ultra-fast modulation pulse scanning laser device and distributed fiber optic detection system according to the present application provided by the present application solves the problem of the existing distributed fiber optic detection system, or the mutual restriction between important indices such as high spatial resolution, long distance and high frequency band.
    [0032] It should be understood that the general description above and the description in detail below are only illustrative by way of example, rather than limiting.
    [0033] Description of figures
    [0034] The technical solution of the present invention will appear more clearly during the detailed description of the appended figures in the examples, and the variants of the figures can be obtained by those skilled in the art without creative work.
    [0035] is a view of the basic structure of an EHz ultra-fast modulation pulse scanning laser device according to an example of the present application;
    [0036] is a view of the basic structure of another EHz ultra-fast modulation pulse scanning laser device according to an example of the present application;
    [0037] is a view of the basic structure of a distributed fiber optic sensing system according to an example of the present application;
    [0038] is a view showing the spatial differential interference of Rayleigh backward scattering light passing through a Michelson interferometer in Figure 3;
    [0039] is a view showing the sequential correspondence between the delayed signal and the original signal in Figure 4;
    [0040] is a view of the basic structure of another distributed fiber optic sensing system according to an example of the present application;
    [0041] is a view of the phase demodulation optical circuit of a 3×3 coupler in FIG. 6;
    [0042] is a block diagram of the phase demodulation algorithm based on the 3×3 coupler according to an example of the present application;
    [0043] is a block diagram of the phase demodulation algorithm based on the orthogonally optimized 3×3 coupler according to an example of the present application;
    [0044] is a view of the basic structure of another distributed fiber optic sensing system according to an example of the present application;
    [0045] is a block diagram of the phase carrier demodulation algorithm according to an example of the present application.
    [0046] Embodiments
    [0047] Illustrative examples will be described in detail below, examples of which are illustrated in the figures. In the description below relating to the figures, unless otherwise indicated, the references in the different figures represent the same or similar elements. The embodiments provided by the present invention are not limited to the embodiments described in the illustrative examples below. They are only examples of devices and methods according to the claims and aspects of the present invention.
    [0048] The laser is a key component of the distributed fiber optic sensing system for high precision dynamic sensing, and the performance parameters of the distributed fiber optic sensing depends on the parameters of the laser device. Considering that the detection range is limited by the coherence length of the laser device in an OFDR system, the present invention provides a new ultra-fast EHz modulation pulse scanning laser device, in order to lengthen the detection distance. of the OFDR system while maintaining high spatial resolution.
    [0049] Fig. 1 is a view of the basic structure of an EHz ultra-fast modulation pulse scanning laser device according to the present example. Shown as Figure 1, the laser device includes a pump laser source 101, a first wavelength division multiplexer 102, a cascaded phase shift optical fiber array 103, a second wavelength division multiplexer 104 and a wavelength selective output device 105.
    [0050] For connection, the output of the pump laser source 101 is connected to the first end of the first wavelength division multiplexer 102, so that most of the pump light can enter the phase-shifting fiber optic grating. in cascade 103 via a coupling by the second end of the first wavelength division multiplexer 102.
    [0051] The cascaded phase-shifting optical fiber grating 103 consists of a plurality of phase-shifting gratings having different center window wavelengths etched onto one or more series-doped optical fibers, the gap between two wavelengths of which of adjacent central windows are preset to a fixed value, or consist of a plurality of phase shift gratings with uniform periodic structure and tightly connected to each other. In particular, the cascaded phase-shifting optical fiber grating 103 can be made by a phase mask displacement method, further, the phase-shifting grating can be etched on a plurality of doped fibers in parallel.
    [0052] Compared with the conventional multi-phase-shift network, the cascaded phase-shift optical fiber network 103 according to the present example has a degree of cascade having little influence on the width of the transmission spectrum, and the internal phase-shift networks open the transmission windows at positions corresponding to wavelengths, the bandwidth of which is similar to that of the single-phase phase shift. In addition, the grating has the advantages such as good transmission wavelength uniformity and stable output power, which promotes stable narrow linewidth power output of the multi-length laser. 'wave.
    [0053] The phase shift gratings in the cascaded phase shift optical fiber grating 103 present the ultra-narrowband transmission peaks, which can ensure a single longitudinal mode in the laser cavity producing the resonances, so as to obtain the characteristics stable for the narrow linewidth single-mode laser, therefore, the cascaded phase-shifting fiber optic grating 103 can emit a plurality of narrow linewidth laser signals under excitation of the pump laser source 101. For example, according to In the present example, an erbium-doped optical fiber is etched with 20 phase shift gratings, the interval between two adjacent central window wavelengths of which is equal to 0.2 nm, i.e. the interval between the wavelengths of the central window λ 1 , λ 2 , λ 3 , λ 4 , λ 5 , λ 6 .... λ 19 , λ 20 is 0.2 nm, so as to obtain a laser light having a difference of fixed wavelength of 0.2 nm and a wavelength range from 1548 nm - 1551.8 nm in the frequency domain. It should be noted that the wavelength interval of the phase shift grating below is not limited to 0.2 nm and can be another value. However, to take into account the bandwidth of the phase shift grating and to avoid overlapping, the wavelength interval in this example is specified to be equal to or greater than 0.2. Nm.
    [0054] In addition, the laser light emitted from the cascaded phase shifting optical fiber array 103 is sent to the second wavelength division multiplexer 104 via the third end of the first wavelength division multiplexer 102, and the second wavelength division multiplexer 104 can simultaneously transmit the optical signals at different wavelengths through different optical channels without interference. Further, according to the present example, an isolator 107 is disposed between the first wavelength division multiplexer 102 and the second wavelength division multiplexer 104, so that the laser light emitted from the first wavelength division multiplexer wavelength division 102 can only be transmitted in one direction along the output direction in the path of the optical fiber, so as to effectively avoid the affection on the output stability of the laser by the effects of backward reflection and scattering, or to avoid damage to the laser device caused by reflected light entering the doped optical fiber through a wavelength division multiplexer.
    [0055] Further, according to the present example, a signal amplifier 108 is disposed between the first wavelength division multiplexer 102 and the second wavelength division multiplexer 104 for amplifying optical signals, wherein one end of signal amplifier 108 is connected to the output of isolator 107, and the other end of signal amplifier 108 is connected to one end of second wavelength division multiplexer 104. absence of the isolator 107, one end of the signal amplifier 108 is connected to the third end of the first wavelength division multiplexer 102. In particular, the signal amplifier 108 can be selected from a erbium-doped optical fiber, a ytterbium-doped fiber amplifier and the like depending on the wavelength of the laser light emitted from the cascaded phase-shifting optical fiber array 103.
    [0056] The wavelength selective output device 105 according to the present example includes a plurality of Electro-optic Modulation Crystals (EOMs) and a controller connected to a plurality of electro-optic modulators, wherein the laser light emitted by each output channel corresponding to each wavelength of the second wavelength division multiplexer 104 is transmitted respectively to one of the electro-optical modulators, and the electro-optical modulators operate under control of the signal emitted by the controller, to orderly trigger one of the electro-optical modulators according to the predefined time interval for a predefined duration and to form a wavelength sequence at the predefined time interval in a time domain. Therefore, the above multi-wavelength laser light can be ultra-fast modulated by a time-domain control method based on an electro-optical modulator, so as to obtain a pulse conversion light. internal frequency which is continuously composed by a plurality of pulsed lights with linearly increasing frequencies.
    [0057] For example, when the command signal emitted by the controller is at a low electrical level, the EOM does not emit anything, on the contrary, when the command signal emitted by the controller is at a high electrical level, the EOM emits. Assuming that the second wavelength division multiplexer 104 emits laser light at 20 wavelengths, and each wavelength output channel is connected to a corresponding EOM, the controller controls the corresponding channel ctl1 to the laser light at the first wavelength at a high level for 0-5 ns, drives the ctl2 channel corresponding to the second wavelength at a high level for 5 ns-10 ns, and so on, disposes laser light at 20 wavelengths in a pulse width of 100 nanoseconds at a uniform time interval, to form an ultra-fast EHz modulation for the laser device.
    [0058] It should be noted that said wavelength selective output device 105 is not limited to the electro-optical crystal and controller modulation mode, and can be in any other way provided that it can allow laser light multi-wavelength output from the second wavelength division multiplexer 104 to be output in order at the preset time interval, so as to form a sequence of wavelengths at the preset time interval eg, acousto-optical modulation or the like, however electro-optical modulation has the advantage of a higher modulation frequency. Further, the doped optical fiber according to the present example is an active fiber obtained by doping various rare-earth ions in an optical fiber substance, and may be an erbium (Er) doped optical fiber, a ytterbium (Yb ) or a fiber doped with thulium (Tm); the corresponding pump source is a semiconductor laser device whose center wavelength of the output laser light matches the absorption wavelength of the doped optical fiber, wherein the center wavelength of erbium (Er) doped optical fiber is 980 nm or 1480 nm, the center wavelength of ytterbium (Yb) doped optical fiber is 915 nm or 975 nm, and the center wavelength of the thulium (Tm) doped optical fiber is 793 nm or 1560 nm; of course, the pump source can be provided by another laser device or a laser diode capable of emitting the desired pump light.
    [0059] In addition, in order that the internal frequency conversion pulsed light emitted from the wavelength-selective output device 105 can be transmitted in a single optical fiber, the output of the wavelength-selective output device 105 according to the present example is provided with a third wavelength division multiplexer 106, in which the laser wavelength range based on the cascaded phase shift optical fiber network 103 is short, therefore, the second multiplexer wavelength division multiplexer 104 and the third wavelength division multiplexer 106 according to the present example may be a dense type wavelength division multiplexer.
    [0060] Further, the laser device according to the present example can output internal frequency conversion pulse light which is continuously composed by a plurality of the linearly increasing frequency pulse lights, thereby enabling said laser device to be used in a system. fiber-optic distributed detection system, to improve the linear frequency scanning range of the laser source in the fiber-optic distributed detection system and effectively ensure the spatial resolution of the OFDR system; moreover, the coherence length of the laser emitted from the laser device can be extended based on the narrow linewidth characteristic of the laser light emitted from the cascaded phase shift grating and the ultra-fast modulation of the electro-optical modulator, without changing the laser frequency. Therefore, the ultra-fast EHz modulation pulse scanning laser device according to the present example solves the problem of the existing distributed optical fiber detection system, which is the mutual restriction between important indices such as high spatial resolution , long distance and high frequency band.
    [0061] Fig. 2 is a view of the basic structure of another EHz ultra-fast modulation pulse scanning laser device according to the present example. Shown as Figure 2, the main difference between the ultra-fast EHz modulation pulse scanning laser device provided by the present example and that provided by Example 1 is that: the phase shift optical fiber grating in cascade 103 according to the present example comprises a plurality of phase shift gratings having different central window wavelengths etched on two doped optical fibers in parallel, namely the gratings of the first cascaded phase shifting optical fiber 1031 and the gratings of the second 1032 cascading phase shift optical fiber;
    [0062] For example, the erbium-doped optical fiber of the grating of the first cascaded phase-shifting optical fiber 1031 can be etched with 10 phase-shifting gratings at the interval of 0.4 nm, corresponding to the output wavelengths of λ 1 , λ 3 , λ 5 ...λ 19 , the ytterbium-doped optical fiber of the grating of the second cascaded phase-shifting optical fiber 1032 can be etched with 10 phase-shifting gratings at the interval of 0.4 nm, corresponding to the output wavelengths of λ 2 , λ 4 , λ 6 ...λ 20 , thus, the wavelength interval of the corresponding grating on two ytterbium-doped optical fibers reaches 0.2 nm, i.e. the interval between λ 1 , λ 2 , λ 3 , λ 4 , λ 5 , λ 6 ..λ 19 , λ 20 is 0.2 nm, so that two ytterbium-doped optical fibers in parallel form 20 distributed wavelengths of the feedback laser light. Consequently, a parallel connection makes it possible to avoid overlapping of the wavelengths and therefore to reduce the wavelength output interval.
    [0063] Note that said cascaded phase-shifting optical fiber grating 103 is not limited to the configuration of two cascaded phase-shifting optical fiber gratings in parallel, and the number of the grating may be another, furthermore, the number of phase shift grating etched on the doped optical fiber of each cascaded phase shifting optical fiber grating is not limited to an identical number, it can be a number provided that it can satisfy the following requirements: the difference of two lengths center window waveform of the phase shift grating etched on each doped optical fiber is equal to a first predefined value and the first fixed predefined value is N times the output wavelength interval of the phase shift grating cascaded, where N is the number of cascaded phase shift optical fiber network.
    [0064] Further, the pump laser source 101 can provide sufficient pump energy to produce narrow linewidth laser light with more stable power and lower linewidth drift. The pump laser source 101 according to the present example comprises a first pump laser sub-source 1011 and a second pump laser sub-source 1012, and the first wavelength division multiplexer 102 comprises a first sub-multiplexer with wavelength division 1021 and a second wavelength division sub-multiplexer 1022, wherein the output of the first pump laser subsource 1011 is connected to the first end of the first wavelength division sub-multiplexer. wavelength 1021, and the output of the second pump laser sub-source 1012 is connected to the first end of the second sub-wavelength division multiplexer 1022; the cascade phase shift optical fiber network 103 is connected to the second end of the first wavelength division sub-multiplexer 1021 and the second wavelength division sub-multiplexer 1022 respectively, and the third end of the first wavelength division sub-multiplexer 1021 or the second wavelength division sub-multiplexer 1022 is connected to one end of the second wavelength division multiplexer 104.
    [0065] Based on the inventive design of the above ultra-fast EHz modulating pulse-scanning laser device, the present example provides a distributed fiber optic sensing system comprising an ultra-fast EHz modulating pulse-scanning laser device according to one of the examples above.
    [0066] Furthermore, considering that the static measurement based on the OFDR technique has been well developed today, and that there is no available system to measure high frequency band disturbing signals, this example also provides a distributed optical fiber detection system, to achieve phase information demodulation for disturbing signals.
    [0067] Figure 3 is a view of the basic structure of a distributed fiber optic sensing system according to the present example. Shown as Figure 3, the system includes a 10 EHz ultra-fast modulation pulse scanning laser device, a circulator 20, a sensing optical fiber 30, a coupler 40, a first interference arm 51, a second interference arm 53, rotating Faraday mirrors 53, 54 and a phase demodulator 60.
    [0068] In which the C1 end of the circulator 20 is connected to the output of the ultra-fast EHz modulation pulse scanning laser device 10, the C2 end of the circulator 20 is connected to the detection optical fiber 30, the end C3 of circulator 20 is connected to the first end of coupler 40, the second end of coupler 40 is respectively connected to the first end of first interference arm 51 and second interference arm 53; the other end of the first interference arm 51 and the second interference arm 53 is respectively connected to a rotary Faraday mirror, the length of the first interference arm 51 of which is not equal to that of the second interference arm interference 53; the phase demodulator 60 is connected to the third end of the coupler 40 to demodulate a phase loading caused by a disturbing signal in the detection optical fiber 30. According to the present example, the first interference arm 51, a second arm of Interference 53, the rotating Faraday mirror and the phase demodulator form a structure called the unbalanced Michelson interferometer. According to the present example, the rotation angle of the Faraday rotating mirror FRM is set to 90°, but it is not limited to this value, in order to realize optical signal emission and eliminate the polarization effect.
    [0069] In the present example, the characteristics of the light wave generated by Rayleigh scattering received by the system at any time based on a one-dimensional impulse response model of Rayleigh backward scattering light will be described. A fiber of length L is divided into N diffusion units, with Δl = L / N being the length of the diffusion unit, assuming that each diffusion unit is completely independent, τ 0 =2nfΔl/c is defined as the unit broadcast time. The light entering the detection optical fiber 30 is internal high-coherence frequency conversion pulsed light, which is designed by us and is continuously composed of k ultra-short pulsed lights with linearly increasing frequencies fk, whose l The interval of two frequencies is equal to a fixed value Δf 0 , the pulse width of each frequency is ω and the total pulse width is k*ω. Accordingly, said high coherence internal frequency conversion pulsed light is incident on the sensing optical fiber 30 from 1=0, and the amplitude of the Rayleigh backward scattering signal obtained at the input of the detection optical fiber 30 can be expressed as follows:
    [0070] (1)(1)
    [0071] In formula (1), a m is the Rayleigh backward scattering amplitude at the m scattering point of the optical fiber, τ m is the time delay at the m scattering point of the optical fiber, and the relationship between τm and optical fiber length l m from the input to the diffusion point m is expressed as follows:
    [0072] (2)(2)
    [0073] ≤1, la fonction rectangulaire =1, et en autres cas =0.In the formula (2), c is the vacuum light speed, n f is the refractive index of the optical fiber, and when 0≤≤1, the rectangular function=1, and in other cases=0.
    [0074] Thus, the information on a given point of the optical fiber can be described by the corresponding Rayleigh backward scattering light signal at a given time, and the change of the scattered light can reflect the content in the information on this point .
    [0075] .Further, the backward Rayleigh scattering light produced in the sensing optical fiber 30 enters via the coupler 40 into a Michelson interferometer having a difference in the length of the interference arm, when the difference in the length of the arm s of the interferometer is much less than the length of the interference arm L, at the point corresponding to the difference in length between two adjacent arms of the interferometer in the fiber optic space in one pulse scan cycle, the lights of Rayleigh backward scattering interferes with each other, which is defined as spatial differential interference. Figure 4 is a view showing the spatial differential interference of Rayleigh backward scattering light passing through a Michelson interferometer in Figure 3. Shown as Figure 4, according to the present example, the signal returned from the second arm of interference 53 shorter is the original signal, the signal returned from the first interference arm 51 is the delay signal, and the optical circuit difference between the two is equal to.
    [0076] , l’amplitude du signal de retard peut être exprimé comme le suit :The delay introduced by the interferometer being, the amplitude of the delay signal can be expressed as:
    [0077] (3)(3)
    [0078] Fig. 5 is a view showing the sequential correspondence between the delayed signal and the original signal in Fig. 4; Shown as Figure 3, the time sequence of the delay signal perfectly matches the original signal, i.e. the incident backscattered light signal in the interferometer, when a number of scattering units in the optical fiber of length s is equal to S L , the time sequence of the delay signal satisfies n=m+S L .
    [0079] Thus, the total interfered light intensity received from the interferometer is:
    [0080]
    [0081] (4)
    [0082] , de plus, la différence de phaseφ mns = 4πfn f Δl(n-m)/c+4πfn f s/ cest une variation de puissance de la lumière diffusée vers l’arrière au certain point causée par la perturbation externe et, par conséquent, les informations sur la position, la fréquence et l’intensité de la source sonore peuvent être obtenues en mesurant la courbe du signal d’interférence, par exemple, la chargement de phase causée par le signal perturbant dans la fibre optique de détection 30 peut être démodulée par le démodulateur de phase 60 connecté à la troisième extrémité du coupleur 40.Formula (4) includes the multi-order differential frequency term, moreover, the phase difference φ mns = 4π fn f Δl ( nm ) /c+ 4π fn f s/ c is a change in power of the backscattered light at the certain point caused by the external disturbance and, by therefore, information about the position, frequency and intensity of the sound source can be obtained by measuring the curve of the interference signal, for example, the phase loading caused by the disturbing signal in the detection optical fiber 30 can be demodulated by the phase demodulator 60 connected to the third end of the coupler 40.
    [0083] Further, according to the formula (4), the total interfered light intensity will be filtered by high-pass filtering to obtain a differential frequency component, and based on the associated filter technology developed from radar technology, the received data will be convoluted with a complex conjugate function proportional to the waveform of the signal, in order to achieve pulse compression. Compared with the single frequency OTDR system, the pulse width is reduced to 1/k from the origin, and the spatial resolution of the system is finally satisfied
    [0084] In the frequency response range, the total interfered light intensity will be filtered by low pass filtering to obtain zero difference frequency component, the system can be equivalent to k different frequency OTDR systems operating at time sequence, when the relative phase results are arranged to the time sequence after the phase demodulation, the frequency response range of the system is increased by k times compared to the single frequency OTDR system. In addition, based on the output characteristics of the 10 EHz ultra-fast modulation pulse scanning laser device, the system can realize simultaneous monitoring of long distance, high frequency band signals and high spatial resolution.
    [0085] For the demodulation of the phase difference signal, the present example provides various phase difference demodulation algorithms. Figure 6 is a view of the basic structure of another distributed fiber optic sensing system according to the present example.
    [0086] Shown as Fig. 6, the 10 EHz modulated ultra-fast pulse scanning laser device according to the present example is a laser device based on the 10 EHz modulated ultra-fast pulse scanning laser device, and further using a chopping waveform by AOM (Acousto-optical Modulators, Acousto-Optical Modulator 70), the degree of isolation of the laser device can reach 60 dB. The signal is amplified by a first Ytterbium-80 Doped Fiber Amplifier (Erbium Doped Fiber Amplifier, EDFA), passes the circulator 20 and enters the detection optical fiber 30, then it is amplified by a second doped fiber amplifier into ytterbium of Rayleigh scattering signal 90, and enters unbalanced Michelson interferometer for spatial differential interference, finally it is demodulated by phase demodulator 60 for demodulation of phase information. The phase demodulator 60 comprises three photoelectric detectors (PD1, PD2, PD3), a circulator and a phase demodulation unit.
    [0087] Figure 7 is a view of the phase demodulation optical circuit of a 40 3x3 coupler in Figure 6. Shown as Figure 7, ports 4 and 6 of the 40 3x3 coupler are connected to two optical fibers of different lengths to form an arm length difference and are respectively connected to a rotating Faraday mirror to form two arms of the phase matching interferometer to adjust the phase difference of the phase matching interferometer, so that the Rayleigh scattering lights backwards into adjacent spatial domains form an interference field. The backward Rayleigh scattering light is incident at port 2 of the 40 3×3 coupler via circulator 20 and is split into two optical signals by port 2 of the 40 3×3 coupler. One optical signal enters the port 4 of 40 3×3 coupler, passes the first interference arm 51 and rotating Faraday mirror 52 and finally returns to port 4 of 40 3×3 coupler. The other optical signal enters port 6 of 40 3 coupler × 3, passes the second interference arm 53 and the rotating Faraday mirror 54 and finally returns to port 6 of the 40 3 × 3 coupler. These two optical signals are combined and interfere at the 40 3 × 3 coupler. Rayleigh backscattered interference enters PD1 and PD3 through ports 1 and 3 of 40 3×3 coupler, and enters PD2 through port 2 of 40 3×3 coupler and circulator 20.
    [0088] The light intensity obtained by the three detectors can be expressed as follows:
    [0089] , p=1,2,3(5), p=1,2,3 (5)
    [0090] In formula (5), Φ(t)=ϕ(t)+ψ(t) ; D is the DC component of the interference signal; I 0 is the amplitude of the alternating component of the interference signal; p is the serial number of the optical signal received by the detector, and p=1,2,3; ϕ(t) is the phase difference signal generated by the disturbing signal, rad; ψ(t) is the phase difference signal generated by the environmental noise, rad.
    [0091] Then, the phase demodulation unit performs phase demodulation on the optical signals received by the three detectors. Figure 8 is a block diagram of the phase demodulation algorithm based on the 3 × 3 coupler according to the present example. Shown as Figure 8, assume that A1 - A7 = 1 for ease of derivation.
    [0092] The light intensity signals of 3 channels are added and multiplied by 1/3, and the first output expression of the adder is as follows:
    [0093] (6)(6)
    [0094] I 1 - I 3 plus -D respectively to obtain:
    [0095] , , (7),,(7)
    [0096] Eliminate the continuous term, keep the alternative term, and operate a differential on a, b and c to obtain:
    [0097]
    [0098] (8)(8)
    [0099]
    [0100] The result of subtracting the two differential signals is multiplied by the remaining signal to obtain:
    [0101]
    [0102] (9)(9)
    [0103]
    [0104] the sum of a ( ef ), b ( fd ) and c ( de )
    [0105] (10)(10)
    [0106] Given that I 0 changes under the influence of the system, eliminate the change of I 0 , operate a summation on the squares of the three signals:
    [0107] (11)(11)
    [0108] Divide formula (10) by formula (11) to obtain:
    [0109] (12)(12)
    [0110] Operate an integration and output the result to obtain:
    [0111] (13)(13)
    [0112] Since ψ(t) is a slow-changing component, one can filter the slow phase-changing component caused by the environment with a high-pass filter, in order to obtain a disturbing signal, such as the loading of phase ϕ(t) caused by the sound signal.
    [0113] , est substitué dans la formule du signal initial de trois voies du coupleur 40 3 x 3 pour obtenir :In addition, to eliminate the influence of the angle formed by the 40 3x3 coupler and to transform a three-way data operation into a two-way data operation, for the phase demodulation algorithm of the 40 3x3 coupler, the requirements on the internal source are reduced based on FPGA (Field-Programmable Gate Array), in order to improve the performance of real-time operations. The present example further provides an improved phase modulation algorithm of the 3 x 3 coupler 40. Figure 9 is a block diagram of the phase demodulation algorithm based on the orthogonally optimized 3 x 3 coupler according to the present example. example. Shown as figure 9, according to the present example, the known angle of the coupler 40 3 x 3 40,is substituted in the formula of the initial three-way signal of the coupler 40 3 x 3 to obtain:
    [0114]
    [0115] (14)
    [0116] Perform a triangulation on the formula (14) to obtain:
    [0117] (15)(15)
    [0118] et dans la formule (15) pour obtenir :Solve the two orthogonal variablesandin the formula (15) to obtain:
    [0119] （16）（16）
    [0120] The differential result:
    [0121] (17) (17)
    [0122] Multiply and then subtract to get:
    [0123]
    [0124] （18）
    [0125] Perform an addition on the two orthogonal variables to obtain:
    [0126] （19）（19）
    [0127] Divide formula (18) by formula (19) to obtain:
    [0128] (20)(20)
    [0129] Differentiate the formula (20) to obtain:
    [0130] （21）（21）
    [0131] Since ψ(t) is a slow-changing component, one can filter the slow phase-changing component caused by the environment with a high-pass filter, in order to obtain a disturbing signal, such as the loading of phase ϕ(t) caused by the sound signal.
    [0132] Figure 10 is a view of the basic structure of another distributed fiber optic detection system according to the present example; Shown as Fig. 10, a main difference between the distributed optical fiber detection system according to the present example and that provided by the previous example is that: the present example adopts phase carrier demodulation, in which the demodulator phase 60 comprises a photoelectric detector (PD4) and a phase demodulation unit, in addition, the first interference arm 51 is provided with a phase modulator 55.
    [0133] The backward Rayleigh scatter light produced by the optical fiber 30 is incident to the coupler 40 via the circulator 20 and is split into two optical signals by the first port of the 3×3 coupler 40. The one optical signal enters the second port of the coupler 40, passes the first interference arm 51 and the rotating Faraday mirror 52 and finally returns to the coupler 40. The other optical signal enters the third port of the coupler 40, passes the second interference arm 53 and the rotating Faraday mirror 54 and finally returns to the coupler 40. These two optical signals are combined and interfere at the coupler 40. The Rayleigh backscattered interference light enters the photoelectric detector PD4 via the fourth port of the coupler 40.
    [0134] According to the principle of luminous coherence, the luminous intensity I of the photoelectric detector PD4 can be expressed as follows:
    [0135] I= A+Bcos Φ (t) （22）
    [0136] In formula (22): A is the average optical power supplied by the interferometer, B is the amplitude of the interference signal, B=κA, and κ≤1 is the visibility of the interference fringe. Φ (t) is the phase difference of the interferometer. When Φ (t) = Ccosω0t + φ (t) , formula (22) can be expressed as:
    [0137] I=A+Bcos[Ccosω 0 t+φ(t)] （23）
    [0138] In formula (22), Ccosω0t is the phase carrier, C is the amplitude, ω0is the carrier frequency; φ(t) =Dcosωst +Ψ(t), Dcosωst is the phase loading caused by a disturbing signal from the detection optical fiber 30, D is the amplitude, ωs is the frequency of the sound field signal and Ψ(t) is the slow change in the initial phase caused by the environmental disturbances. Expand formula (23) with the Bessel function to obtain:
    [0139] (24) (24)
    [0140] In the formula (24), J n (m) is the value of the Bessel function of order n at the depth of modulation m, by indicating k = 0 and 1, we can obtain the best signal and the double frequency signal .
    [0141] Figure 11 is a block diagram of the phase carrier demodulation algorithm according to an example of the present application. Shown as Figure 11, according to the present example, the phase demodulator 60, i.e. the phase carrier demodulation device (Phase Generated Carrier, PGC) comprises a multiplier, a filter, a differentiator and a integrator. The detector signal is multiplied by the baseband signal in the first multiplier and then enters the first low-pass filter; the signal is sent to the first differentiator, and multiplied by the signal filtered by the second low-pass filter; the signal enters one end of the subtractor, and is subtracted from the multiplied signal in the fourth multiplier. The detector signal is multiplied by the dual frequency signal in the second multiplier and then enters the second low pass filter; the signal is sent to the second differentiator and multiplied by the signal filtered by the first low-pass filter; the signal enters one end of the subtractor, and subtracts from the multiplied signal in the third multiplier. The two signals are sent simultaneously to the subtractor, operated and then sent to the integrator and the high pass filter to demodulate the detection signal. In particular:
    [0142] After expanded with the Bessel function, the I signal from the interferometer output detector is multiplied by the base frequency signal (the amplitude is G) and the double frequency signal (the amplitude is H). To eliminate the cancellation and distortion caused by the change of the external spurious signal, the two signals are subjected to differential cross-multiplication (DCM), and the signals after DCM are converted to the following formula at the end of an amplification differential and integration.
    [0143] B 2 GHJ 1 (C)J 2 (C)φ(t) （25）
    [0144] Substitute φ(t) =Dcosω s t +Ψ (t) in formula (25) to obtain:
    [0145] B 2 GHJ 1 (C)J 2 (C)[Dcosω s t+Ψ(t)] （26）
    [0146] The signal obtained after the integration contains the signal Dcosω s t to be detected and the external environmental information, generally the last one is a slowly changing signal, with a large amplitude, which can be filtered by a high-pass filter, thus the system comes out at the end:
    [0147] B 2 GHJ 1 (C)J 2 (C)Dcosω s t （27）
    [0148] The phase loading signal Dcosω s t caused by the disturbing signal from the detection optical fiber 30 can be solved by the formula (27).
    [0149] The examples in the description are described step by step, and the same or similar parts of the examples may be referred to each other, and each example focuses on the differences from the other examples.
    [0150] The person skilled in the art may obtain other embodiments based on the description and the embodiment. The present application is intended to cover all variations, uses or variation of adaptation of the present invention, which must comply with the general principles of the present invention and relate to the general knowledge or the means known in the conventional technical field and not mentioned by the present invention. The description and examples are for illustrative purposes only, and the scope and spirit of the present invention should be set forth in the claims.
    [0151] It should be understood that the present invention is not limited to the structures described above and shown in the figures, variations and modifications are possible within the scope of the present invention. The scope of the present invention is limited by the claims.
    权利要求:
    Claims (8)
    [0001]
    An ultra-fast EHz modulation pulse scanning laser device, characterized in that, said laser device comprises a pump laser source, a first wavelength division multiplexer, a cascade phase shifting optical fiber array , a second wavelength division multiplexer, a plurality of electro-optical modulators, and a controller connected to the plurality of electro-optical modulators, wherein: the output of the pump laser source is connected to the first end of the first wavelength division multiplexer; The cascade phase-shifting optical fiber network consists of a plurality of phase-shifting networks having different center window wavelengths etched on the doped optical fibers, the interval between two adjacent center window wavelengths of which is preset to a fixed value, and the cascade phase-shifting optical fiber network is connected to the second end of the first wavelength division multiplexer; the third end of the first wavelength division multiplexer is connected to one end of the second wavelength division multiplexer; the laser light emitted from each output channel corresponding to each wavelength of the second wavelength division multiplexer is respectively transmitted to one of the electro-optical modulators; the controller is configured to trigger in order one of the electro-optical modulators according to the predefined time interval for a predefined duration.
    [0002]
    A high-speed EHz modulation pulse scanning laser device according to claim 1, characterized in that, said laser device further comprises an isolator, wherein: one end of the isolator is connected to the third end of the first wavelength division multiplexer and the other end is connected to one end of the second wavelength division multiplexer.
    [0003]
    A high-speed EHz modulation pulse scanning laser device according to claim 1, characterized in that, said laser device further comprises a signal amplifier, wherein: one end of the signal amplifier is connected to the third end of the first wavelength division multiplexer and the other end is connected to one end of the second wavelength division multiplexer.
    [0004]
    A high-speed EHz modulation pulse scanning laser device according to claim 1, characterized in that, said cascade phase-shifting optical fiber array consists of N doped optical subfibers in parallel, with N≥2, in which : said doped optical fiber of the cascade phase-shifting optical fiber sub-array is etched with a plurality of phase-shifting networks having different center window wavelengths, the interval between two adjacent center window wavelengths of which is preset to the first fixed value; the first predefined fixed value is N times the output wavelength interval of the phase shifting optical fiber network in cascade.
    [0005]
    Ultra-fast EHz modulation pulse scanning laser device according to any one of claims 1 to 4, characterized in that, said pump laser source comprises a first pump laser sub-source and a second pump laser sub-source , and the first wavelength division multiplexer comprises a first wavelength division sub-multiplexer and a second wavelength division sub-multiplexer, wherein; the output of the first pump laser sub-source is connected to the first end of the first wavelength division sub-multiplexer, and the output of the second pump laser sub-source is connected to the first end of the second wavelength division sub-multiplexer; said cascade phase-shifting optical fiber network is connected respectively to the second end of the first wavelength division sub-multiplexer and to the second end of the second wavelength division sub-multiplexer; the third end of the first or second wavelength division sub-multiplexer is connected to one end of the second wavelength division multiplexer.
    [0006]
    A high-speed EHz modulating pulse scanning laser device according to any one of claims 1 to 4, characterized in that the interval between two adjacent center window wavelengths is equal to or greater than 0.2 nm.
    [0007]
    A distributed optical fiber detection system, characterized in that it comprises an ultra-fast EHz modulation pulse scanning laser device according to any one of claims 1 to 6.
    [0008]
    A distributed optical fiber detection system according to claim 7, characterized in that, said system further comprises a circulator, a detection optical fiber, a coupler, a first interference arm, a second interference arm, a mirror Faraday rotary and a phase demodulator, in which: the output of the high-speed EHz modulation pulse scanning laser device is connected to the first end of the circulator, the second end of the circulator is connected to the detection optical fibers, and the third end of the circulator is connected to the first end coupler; the second end of the coupler is respectively connected to one end of the first interference arm and the second interference arm, and the other end of the first interference arm and the second interference arm is respectively connected to the Faraday rotating mirror , whose length of the first interference arm is not equal to that of the second interference arm; the phase demodulator is connected to the third end of the coupler to demodulate a phase loading caused by a disturbing signal in the detection optical fiber.
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    同族专利:
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    US20210010834A1|2021-01-14|
    CN110160573A|2019-08-23|
    引用文献:
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    US11248952B2|2019-08-13|2022-02-15|Laser Institute of Shandong Academy of Science|Fiber distributed acoustic sensing system|US6195200B1|1998-02-18|2001-02-27|Lucent Technologies Inc.|High power multiwavelength light source|
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    CN111595365A|2020-07-06|2020-08-28|山东省科学院激光研究所|Multi-wavelength laser for synchronously monitoring ocean temperature and pressure|
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    CN201910611291.0A|CN110160573A|2019-07-08|2019-07-08|Ai Hezi ultrafast modulation pulse scan laser and distributed optical fiber sensing system|
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